In U.S. patent application Ser. No. 12/603,087 filed Oct. 21, 2009 (US Patent Publication No. 2010-0098818 published Apr. 22, 2010), Ser. No. 12/923,897 filed Oct. 13, 2010 (US Patent Publication No. 2011-0038993 published Feb. 11, 2011) and Ser. No. 12/998,422 filed Jun. 1, 2011 (US Patent Publication No. 2011-0236556 published Sep. 29, 2011), assigned to the assignee hereof and the disclosures of which are incorporated herein by reference, there is described the production of soy protein products having a protein content of at least about 60 wt % (N×6.25) on a dry weight basis (d.b.), preferably at least about 90 wt %, which produce transparent, heat stable solutions at low pH values and which may be used for protein fortification of soft drinks, as well as other aqueous systems, without precipitation of protein.
The soy protein product is produced by extracting a soy protein source with an aqueous calcium chloride solution to cause solubilization of soy protein from the protein source and to form an aqueous soy protein solution, separating the aqueous soy protein solution from residual soy protein source, optionally diluting the soy protein solution, adjusting the pH of the aqueous soy protein solution to a pH of about 1.5 to about 4.4, preferably about 2 to about 4, to produce an acidified clear soy protein solution, optionally concentrating the aqueous clear protein solution while maintaining the ionic strength substantially constant by using a selective membrane technique, optionally diafiltering the concentrated soy protein solution, and optionally drying the concentrated and optionally diafiltered soy protein solution.